@fisherlawyer1 when in the U.K. you can call, text and use data for anything you like as long as you have the appropriate funding in place ie Airtime Credit and / or a Goodybag.
As you are not obliged to have only one or the other but can have both it is up to you how you use the phone.
So for example if you generally use a goodybag while here to make U.K. calls but also have some Airtime Credit then you can connect to Spain via apps using data from the bag but you could also call or text them using your credit at the following rates:
Landline - 2p per min
Mobile - 9p per min
Text - 8p
MMS - 16p
When you leave the U.K. to go to Spain you are then covered by the EU Roam Like at Home regulations and so could continue to use a goodybag for as long as your eligibility lasted.
Your right to use the goodybag is based on your U.K. vs non-U.K. usage over a rolling 120 day period so the headline figure is that you can have up to a maximum of 63 days use of a bag before your eligibility runs out. However it does require you to be aware of how long you spend in and out of the U.K. over time as it is not a straight 60 days every time you go to the EU as some people think!
All that said even if you run out of the right to use the allowances included in your bag and have to start using your Airtime Credit just having a live bag does give you access to the cheaper EU defined PAYG rates of 3.2p per min, 1p per text and 0.47p per MB.
So you may find that having a bag (even the £5 one) while in Spain might work for you.
I hope that has helped but if you want any more information do come back and ask.